The present invention is directed to mechanical locking of a metal tube to a metal hose fitting, and more particularly to coupling of a metal tube to a fitting at the end of a hose or other constituent part in a vehicle fluid system such as an automotive brake system.
Mechanical tube coupling arrangements in vehicle fluid systems, such as automotive brake systems, must be leak resistant at high internal fluid pressure on the order of several thousand psi. Tube fittings that employ threaded tube nut joints tend to leak at high fluid pressure because of improper tightening torque and unsatisfactory sealing surface conditions. The fluid tubes are located in areas that can be subjected to corrosive materials such as salt, and it has become the practice to coat the metal tubes for enhanced corrosion resistance. Consequently, the tube end fitting must be such as not to scratch or remove the coating, which can provide a site for corrosion attack. It is therefore a general object of the present invention to provide a tube coupling arrangement and a method of manufacture that do not damage a corrosion resistant coating on the fluid tube, that withstand leakage at elevated fluid pressure, that employ otherwise conventional machining and processing techniques, and that employ a reduced number of parts and therefore exhibit reduced manufacturing costs.
A tube coupling arrangement in accordance with presently preferred embodiments of the invention includes a metal fitting having an end, an internal through passage, and a conical groove that extends radially and axially outwardly from the through passage away from the tube end and into the body of the fitting. A metal tube is received in the through passage of the fitting, and has an outwardly flared conical end disposed in the conical groove within the fitting. The end of the fitting is plastically deformed around the tube in sealing engagement with an external surface of the tube and firmly to hold the tube end in sealing engagement with the conical groove. In the preferred embodiments of the invention, the conical end of the tube is either single-thickness or is doubled upon itself so that the conical end has a double tube wall thickness within the internal groove in the fitting. Barbs preferably are formed in the flared end of the tube to prevent rotation of the tube within the fitting. The coupling arrangement of the present invention thus eliminates potential fluid leak paths associated with threaded coupling joints, and potential damage to the corrosion coating on the tube.
A method of securing a cylindrical metal tube to a metal constituent part, such as a fitting, in accordance with another aspect of the present invention includes the steps of flaring an end of the tube to form a conical end configuration, inserting the conical tube end configuration into a fitting to abut a shoulder within the fitting, and then securing the fitting to the tube by plastically deforming the fitting around the external surface of the tube end. The tube end may be folded upon itself prior to or during the step of flaring the tube end, so that the tube end has either a single or double wall thickness in the area of abutment against the shoulder within the fitting. Barbs are preferably formed in the flared end of the tube prior to insertion of the tube into the fitting to prevent rotation of the tube within the fitting after the fitting is crimped over the tube end.